Various methods have been disclosed heretofore for the disposal of sewage sludge wastes. For the past several years, it has been customary in areas along the Eastern Seaboard, and particularly in the New York City area, to load sewage sludge into barges which are towed out to sea and dumped into the ocean. Alternative methods of disposal include dewatering the sewage sludge by centrifuges and dumping the dewatered sewage sludge solids in land fill areas. Dumping at sea is becoming more and more restricted as a disposal method while, at the same time, metropolitan areas are rapidly running out of available land fill sites.
Incineration of sewage sludge solids has been proposed but is not an attractive method of disposal due to the water content of moist centrifuged sludges or filter cake solids, which typically contain 65 to 75 percent water after concentration by conventional filtering or centrifuging methods. Also, the presence of toxic heavy metals in metropolitan sewage sludges militates against incineration on two counts: the more volatile heavy metals tend to be discharged into the atmosphere with a large volume of combustion products and excess air, while the less volatile heavy metals are discharged with the leachable incinerator ash whence the toxic heavy metals may eventually leak into the drinking water supply. It has been proposed in U.S. Pat. No. 3,687,646 to Teichmann et al to mix sewage sludge solids with fuel oil and to convert the mixture to useful fuel gas or synthesis gas by reaction with oxygen and steam in a closed reaction zone which is free from packing or catalyst. The reaction is carried out at an autogenous temperature in the range of from about 1800.degree. to about 2600.degree. F. effecting the partial oxidation of the feed mixture to industrially useful fuel gas or synthesis gas.
The art of pressing coal into briquettes is well known. The objective has been principally to utilize coal fines by compacting them into a more easily handled and stored fuel. The compaction or pelleting of municipal refuse together with waste coal products also has been proposed. Jackman in U.S. Pat. No. 3,910,775 disclosed the briquetting of coal including coal fines with organic wastes. In this patent, minor quantities of acidic coal fines are apparently used for the purpose of reducing the pH of a sewage stream filtered through the prepared briquettes so as to precipitate phosphates present in the waste water.
My U.S. Pat. Nos. 4,225,457; 4,152,119 and 4,052,173, which are incorporated herein by reference and made a part hereof, disclose the production of briquettes from sewage sludge and municipal solid wastes and their gasification in a moving bed gasifier. The briquettes are formed from a well blended mixture of sewage sludge, shredded organic solid wastes, especially municipal solid wastes, and crushed caking coal including coal fines. In those patents, dewatered sewage sludge is included in the mixture as a binder to aid in the formation of the briquettes.